The dynamic structure factor of lithium-diborate glass has been measured at several values of the momentum transfer $Q$ using high resolution inelastic x-ray scattering. Much attention has been devoted to the low $Q$-range, below the observed Ioffe-Regel crossover qco{}$simeq$ 2.1 nm$^{-1}$. We find that below qco{}, the linewidth of longitudinal acoustic waves increases with a high power of either $Q$, or of the frequency $Omega$, up to the crossover frequency OMco{} $simeq$ 9 meV that nearly coincides with the center of the boson peak. This new finding strongly supports the view that resonance and hybridization of acoustic waves with a distribution of rather local low frequency modes forming the boson peak is responsible for the end of acoustic branches in strong glasses. Further, we present high resolution Brillouin light-scattering data obtained at much lower frequencies on the same sample. These clearly rule out a simple $Omega^2$-dependence of the acoustic damping over the entire frequency range.
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